Karl, the 2010 Olympic silver medallist, damaged ligaments in his left ankle in a motorcycle accident, while Grabner tore his left ACL and meniscus at the national championships in St. Gallenkirch.
Both are now back out on their boards on the Stubai glacier.
"My ankle did hurt a lot when I did my first turns on the board a few weeks ago. But now it's getting better and better," said Karl.
"I actually get the feeling for my board back. And also the gear is looking pretty good."
Veteran Grabner said: "I'm truly motivated to be back on snow and happy that our season starts pretty late. Otherwise, it would have been very stressful for me."
The new campaign kicks off in Carezza, Italy on December 21.